I first became aware of the process of head shrinking (tsantsas) at the Ripley's Believe it or not museum in NYC. Common amongst tribes in the upper amazon region of Ecuador and Peru, these strange palm sized human heads have undergone a unique shrinking process that can be traced back to 1100BC. You may be familiar with the historical term of head hunting - "a practice of taking and preserving a person's head after killing that person", well the Jivaro tribes took this concept to a whole new level.
During battles with other tribes, Jivaro warriors would kill the enemy and decapitate them, claiming their enemies' heads as symbols of bravery and displaying them as war trophies.
They start their work by making an incision in the neck and up the back of the head to peel the skin and hair away from the skull. The brain and skull would then be discarded as an offering to the pani, or anaconda, which the tribes considered to be a spirit helper.
The eyes and mouth were sewn shut with cotton strings, the lips skewered closed with wooden pegs and the face was blackened with vegetable dye to prevent the soul from escaping the tsantsas and seeking revenge on the killer. In addition keeping its thin leathery skin well preserved.
To shrink the head, the skin was immersed in hot water and left to simmer for about an hour and a half to two hours. Hot sand was later poured into the water, and was repeated several times over a period of months. Too short a time would result in the head not shrinking properly, while leaving the head too long in the pot would cause the hair on the head to fall out. When the head was removed from the pot, it would be reduced by two-thirds of its original size. 
Facial features were moulded by hand after each treatment. After this, the head was dried so that it would continue to shrink. Small rocks heated by a fire were used to fill the cavity of the head. When the head becomes too small for the stones, heated sand was used instead. In addition, heated rocks were applied to the outside of the head to maintain the features. This process lasted several days, after which the pegs through the lips were removed and replaced with dangling cotton cords.